This title appears in the Scientific Report :
2013
Please use the identifier:
http://hdl.handle.net/2128/3696 in citations.
Observation- and model-based study of the extratropical UT/LS
Observation- and model-based study of the extratropical UT/LS
Coupling between processes of different nature, as radiation, dynamics and chemistry, in the upper troposphere and lower stratosphere (UT/LS) makes this region highly sensitive to climate change. This thesis addresses the climatological representativeness of trace gases measured in–situ within the U...
Saved in:
Personal Name(s): | Kunz, Anne (Corresponding author) |
---|---|
Contributing Institute: |
Stratosphäre; ICG-1 |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
2010
|
Physical Description: |
XII, 120, XII S. |
Dissertation Note: |
Univ. Wuppertal, Diss., 2009 |
ISBN: |
978-3-89336-603-3 |
Document Type: |
Book |
Series Title: |
Schriften des Forschungszentrums Jülich. Reihe Energie und Umwelt / Energy und Environment
54 |
Subject (ZB): | |
Link: |
OpenAccess |
Publikationsportal JuSER |
Coupling between processes of different nature, as radiation, dynamics and chemistry, in the upper troposphere and lower stratosphere (UT/LS) makes this region highly sensitive to climate change. This thesis addresses the climatological representativeness of trace gases measured in–situ within the UT/LS as well as their temporal variability. Possible atmospheric processes which may contribute to the maintenance of tropopause related structures in the extratropics are discussed. These studies are based on the closely linked use of experimental data, statistical analyzes and atmospheric models. In the first part of this thesis, a statistical analysis is presented for the comparability of water vapor (H$_{2}$O) and ozone (O$_{3}$) data sets sampled during the SPURT aircraft campaigns and the MOZAIC passenger aircraft flights. A different variability character in both trace gas data sets is evident by a variance analysis. While the SPURT H$_{2}$O data can only resolve atmospheric processes variable on a diurnal or synoptic time scale, MOZAIC H$_{2}$O data also resolve processes on an inter–seasonal and a seasonal time scale. The SPURT H$_{2}$O data set does not represent the full MOZAIC H$_{2}$O variance in the UT/LS for climatological investigations, whereas the variance of O$_{3}$ is much better represented. SPURT H$_{2}$O data are better suited in the stratosphere, where the MOZAIC relative humidity sensor loses its sensitivity. This is the first analysis which addresses the ability of measured trace gases to detect the atmospheric variability in the UT/LS. In the second part of the thesis, the relationship between the static stability N$^{2}$ within the tropopause inversion layer (TIL) in the extratropics and the atmospheric mixing in that region is investigated using the SPURT O$_{3}$ and CO observations. For this purpose N$^{2}$ is determined from ECMWF fields. A new measure of mixing degree based on O$_{3}$–CO tracer correlations is developed. It is found that high N$^{2}$ is related to an enhanced mixing degree in the extratropical mixing layer. A temporal variance analysis of N$^{2}$ at the particular SPURT measurement locations suggests that the processes responsible for the composition of the TIL occur on a seasonal time scale. The Reading radiative transfer model is used to simulate the influence of a change in O$_{3}$ and H$_{2}$O vertical gradients on the temperature gradient and thus on the static stability above the tropopause. Zonal and time mean ECMWF O$_{3}$ and H$_{2}$O profiles, which are used as reference mixed profiles, are perturbed to represent idealized non–mixed profiles in the atmosphere. The results of the simulations show that N$^{2}$ increases with enhanced mixing degree near the tropopause and a temperature inversion develops. In the idealized case of non–mixed profiles the TIL vanishes. H$_{2}$O plays the dominant role in maintaining the temperature inversion and the TIL structure compared to O$_{3}$. Here, the two different atmospheric features, i.e., the mixing layer and the TIL in the extratropics, are discussed together for the first time. In the last part of the thesis, the gradient of the potential vorticity with equivalent latitude is used to determine the core of the jet streams and its meridional boundaries on different middle world isentropes (300–380 K). The jet cores represent a physical boundary on the isentropes between the troposphere at lower latitudes and the stratosphere at higher latitudes. Thus, a PV gradient tropopause related to the isentropic gradient of the potential vorticity is proposed, which may represent the separation between the two atmospheric reservoirs troposphere and stratosphere in a more appropriate manner than the use of a particular value of PV. Dependent on season the zonal and time mean PV at this newly defined tropopause varies between 2.0 PVU–3.5 PVU and decreases from lower toward higher latitudes in the northern hemisphere. This decrease is sharper on the southern hemispheres compared to the northern hemisphere. The analysis indicates that as the dynamical tropopause the commonly used 2 PVU threshold is too low most of the time. With the help of tracer correlations and a new coordinate system, using equivalent latitude relative to the jet core, the isentropic distribution and transition of the static stability across the PV gradient tropopause is analyzed. This transition is more pronounced during winter than summer on each isentrope in the lowermost stratosphere, which is consistent with the transport barrier at the jet streams related to the sharpness of the tropopause. |